The effect of autophagy and mitochondrial fission on Harderian gland is greater than apoptosis in male hamsters during different photoperiods.

Photoperiod is an important factor of mammalian seasonal rhythm. Here, we studied morphological differences in the Harderian gland (HG), a vital photosensitive organ, in male striped dwarf hamsters (Cricetulus barabensis) under different photoperiods (short photoperiod, SP; moderate photoperiod, MP; long photoperiod, LP), and investigated the underlying molecular mechanisms related to these morphological differences. Results showed that carcass weight and HG weight were lower under SP and LP conditions. There was an inverse correlation between blood melatonin levels and photoperiod in the order SP > MP > LP. Protein expression of hydroxyindole-O-methyltransferase (HIOMT), a MT synthesis-related enzyme, was highest in the SP group. Protein expression of bax/bcl2 showed no significant differences, indicating that the level of apoptosis remained stable. Protein expression of LC3II/LC3I was higher in the SP group than that in the MP group. Furthermore, comparison of changes in the HG ultrastructure demonstrated autolysosome formation in the LP, suggesting the lowest autophagy level in under MP. Furthermore, the protein expression levels of ATP synthase and mitochondrial fission factor were highest in the MP group, whereas citrate synthase, dynamin-related protein1, and fission1 remained unchanged in the three groups. The change trends of ATP synthase and citrate synthase activity were similar to that of protein expression among the three groups. In summary, the up-regulation of autophagy under SP and LP may be a primary factor leading to loss of HG weight and reduced mitochondrial energy supply capacity.

The increase in fat content in the warm-acclimated striped hamsters is associated with the down-regulated metabolic thermogenesis.

It has been well known that metabolic thermogenesis plays an important role in the thermoregulation of small mammals under different temperatures, while its role in fat accumulation is far from clear. In the present study, several physiological, hormonal, and biochemical measures indicative of metabolic thermogenesis were measured in the weaning striped hamsters after acclimated to a warm condition (30°C) for 1, 3 and 4months. The warm-acclimated groups significantly decreased energy intake, and simultaneously decreased nonshivering thermogenesis compared to those housed at 21°C. Body fat content increased by 29.9%, 22.1% and 19.6% in the hamsters acclimated to 1, 3 or 4months, respectively relative to their counterparts maintain at 21°C (P<0.05). The cytochrome c oxidase (COX) activity of brain, liver, heart and skeletal muscle, and the ratio of serum tri-iodothyronine to thyroxine significantly decreased in warm-acclimated groups compared with 21°C group. COX activity and uncoupling protein 1 (UCP1) mRNA expression of brown adipose tissue (BAT) were significantly down-regulated under the warm conditions. COX activity of BAT, liver, heart and muscle were significantly negatively correlated with body fat content, and the correlation between UCP1 expression and body fat content tended to be negative. These findings suggest that the decrease in the energy spent on metabolic thermogenesis plays an important role in the fat accumulation. The attenuation of COX and UCP1-based BAT activity may be involved in body fat accumulation in animals under warm conditions.

Trunk and paw pad skin morphology of the African giant pouched rat (Cricetomys gambianus, Waterhouse-1840)

The gross morphology and histology of the skin of the trunk and paw pads in the African giant pouched rat were investigated to evaluate their role in the adaptation of the rodent to its subterranean environment. Samples were stained with haematoxylin and eosin, Masson’s trichrome, Alcian blue, Verhoeff's haematoxylin counterstained with Van Gieson, and Weigert’s haematoxylin counterstained with Picro-Ponceau stains. Dorsally, fur covering the skin was loosely folded. Fur covered the entire trunk to the level of the radiocarpal and talocrural joints of the forelimb and hindlimbs, respectively. Skin of the dorsum was paler than its grey-coloured fur, while skin of the ventrum was dirty white. There were more hair follicles dorsally then ventrally. The manus and pes had five and six paw pads, respectively. Keratinocytes in the epidermis of the paw pads decreased in number and lost their cellular contents as they migrated towards the stratum lucidum. Metatarsal pads had a significantly (P < 0.001) thicker stratum corneum than metacarpal pads. Elastic fibres were observed in the metatarsal pads. Other results and additional information from the literature were integrated to propose the effect of the structures on the adaptation of the African giant pouched rat to its subterranean environment and tropical climate

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When homologous cusps display non-homologous wear facets: An occlusal reorganization ensures functional continuity during dental evolution of Murinae (Rodentia, Mammalia).

OBJECTIVE: This study was designed to interpret the differences between the occlusal relationships in the murine rodents and those in their Miocene "cricetodont" ancestors. It aimed at understanding the functional transformations that led to the emergence of the peculiar chewing motion of the Murinae, associating forwardly directed masticatory movements to cusp interlocking, a trait unique amongst mammals. METHODS: Microwear analyses and simulations of occlusion achieved with size-increased 3D printings of teeth crafted from 3D data obtained by X-ray synchrotron microtomography at the European synchrotron radiation facility allow us to carefully interpret the occlusal relationships in Muroidea. RESULTS: A rotation of the direction of the chewing movements occurred from "Cricetodontinae" to Murinae. This rotation emerged without any cusp removal contrary to previous interpretations, by the way of an occlusal reorganization involving a loss of contacts between some cusps, offset by a contact with other cusps. This new organization was already present in the early and middle Miocene genus Potwarmus. CONCLUSION: Molar tooth evolution in Murinae was characterized by the preservation and the reshaping of the primitive muroid cusps, the acquisition of supplementary cusps, and changes in the contacts between the opposite cusps. During evolution, changes of cusp patterns in upper and lower molar teeth are coordinated in order to retain a functional occlusion. Because of this functional constraint, one cusp was supposed to more likely occlude with the same opposite cusps during evolution, and therefore homologous cusps would always carry homologous attrition facets. Evolution of Murinae proves that functional continuity can also be preserved through changes in occlusal relationships independently from cusp removal.

Ultrastructural changes of posterior lingual glands after hypoglossal denervation in hamsters.

Posterior lingual glands consist of two sets of minor salivary glands that serve important functions in oral physiology. To investigate the hypothesis that the hypoglossal nerve provides sympathetic innervation to the posterior lingual glands, we examined ultrastructural changes in the glands following hypoglossal denervation. In the posterior deep lingual glands (of von Ebner), the serous acinar cells showed a decrease in the number of secretory granules and an increase in lipofuscin accumulation. The ratios of cells containing lipofuscin granules were 11.39, 36.49 and 50.46%, respectively, of the control, 3- and 7-day post-axotomy glands (P < 0.001). Intraepithelial phagocytotic activity was increased. The mucous acinar cells in the posterior superficial lingual glands (of Weber) also showed degenerative changes after hypoglossal denervation. One week after nerve transection, marked cytoplasmic vacuolation and fragmentation of organelles were frequently observed. Degenerative changes were also found in unmyelinated axons associated with the glands. We provide the first evidence of the structural and functional connections between the sympathetic component of the hypoglossal nerve and posterior lingual glands.

Parameters of microcirculation in hamster buccal pouches under conditions of reduced systemic blood pressure.

Laser Doppler flowmetry studies showed that blood flow in the microcirculation bed of paired buccal pouches in hamsters decreased under conditions of reduced systemic blood pressure and this decrease is more pronounced in the left pouch. The transition of the circulatory bed to the new state is step-wise in the left pouch and continuous in the right one.

Evidence for the disproportionate mapping of olfactory airspace onto the main olfactory bulb of the hamster.

Olfactory receptor neurons (ORNs) project to the rodent main olfactory bulb (MOB) from spatially distinct air channels in the olfactory recesses of the nose. The relatively smooth central channels of the dorsal meatus map onto the dorsal MOB, whereas the highly convoluted peripheral channels of the ethmoid turbinates project to the ventral MOB. Medial and lateral components of each projection stream innervate the medial and lateral MOB, respectively. To ascertain whether such topography entails the disproportionate representation seen in other sensory maps, we used disector-based stereological techniques in hamsters to estimate the number of ORNs associated with each channel in the nose and the number of their targets (glomeruli and mitral and tufted cells) in corresponding divisions of the MOB. Each circumferential half of the MOB (dorsal/ventral, medial/lateral) contained about 50% of the 3,100 glomeruli and about 50% of the 160,000 mitral and tufted cells per bulb. We found equivalent numbers of ORNs with dendritic knobs in the medial and lateral channels (4.5 million each). However, the central channels had only 2 million knobbed ORNs, whereas the peripheral channels had 7 million. Thus, there is a disproportionate mapping of the central-peripheral axis of olfactory airspace onto the dorsal-ventral axis of the MOB, encompassing a greater than threefold variation in the average convergence of ORNs onto MOB secondary neurons. We hypothesize that the disproportionate projections help to optimize chemospecific processing by compensating, with differing sensitivity, for significant variation in the distribution and concentration of odorant molecules along the olfactory air channels during sniffing.

A striated muscle on the hard palate of rodents and rabbits.

Summary A striated muscle of the hard palate has been previously described in some rodents and rabbits. It is not termed in the official veterinary anatomical nomenclature. The aim of this work was to verify the existence of this muscle. Heads of the golden hamster (Mesocricetus auratus), the guinea pig (Cavia aperea f. porcellus), the laboratory rat (Rattus norvegicus var. alba), the field vole (Microtus agrestis) and the domestic rabbit (Oryctolagus cuniculus f. domesticus) have been dissected. Moreover, histological sections have been prepared from heads of the field vole. In all species under study, we could detect a striated muscle of the hard palate composed of an anterior and a posterior muscle. The anterior muscle originated on the os incisivum and diverged in anterior, lateral and posterior directions. The posterior muscle originated on the processus palatinus maxillae and verged into the m. buccinator. Inter-species differences could be detected in shape and position of the muscle. The palatal muscle was innervated by the ramus buccalis of the facial nerve. Whether this muscle should be classified as an individual facial muscle or as a part of the m. buccinator remains to be discussed.

Marcadores histoquímicos de cancerización de campo en la mucosa bucal / Histochemical markers of field cancerization in the oral mucosa

El término "cancerización de campo" en la cavidad bucal se utiliza para definir a una mucosa en la que existen cambios subclínicos de malignidad debido a los cuales posee un riesgo aumentado de que se produzcan en ella tumores en forma uni o multifocal. Se han postulado métodos diversos para la detección temprana de la cancerización de campo, entre los cuales los de mayor utilidad potencial son aquellos que puedan aplicarse al material de biopsias para estudio histopatológico de rutina. En este trabajo se analiza la eficacia de tres biomarcadores histoquímicos de malignidad para detectar cancerización de campo en un modelo experimental de cáncer bucal: morfometría de regiones organizadoras de nucleolo (NORs), análisis de la ploidia y marcación inmunohistoquímica del factor de crecimiento fibroblásticos-2 (FGF-2). Los tres detectaron variaciones en epitelios cancerizados antes de que se manifiesten alteraciones histológicas. Dado que presentan diferencias en cuanto a su facilidad de aplicación y diferente sensibilidad para la detección de malignidad, el uso conjunto de éstos o más marcadores podría aumentar la certeza en la detección del potencial de malignidad (AU)

Crossed and uncrossed retinal projections to the hamster circadian system.

The hamster suprachiasmatic nucleus (SCN), site of the circadian clock, has been thought to be equally and completely innervated by each retina. This issue was studied in animals that had received an injection of the tracer cholera toxin subunit B (CTb) conjugated to Alexa 488 into the vitreous of one eye, with CTb-Alexa 594 injected into the other. Retinal projections to the SCN and other nuclei of the circadian system were simultaneously evaluated by using confocal laser microscopy. Each retina provides completely overlapping terminal fields throughout each SCN. Although SCN innervation by the contralateral retina is slightly denser than that from the ipsilateral retina, there are distinct SCN regions where input from one side is predominant, but not exclusive. A dense terminal field from the contralateral retina encompasses, and extends dorsally beyond, the central SCN subnucleus identified by calbindin-immunoreactive neurons. Surrounding the dense terminal field, innervation is largely derived from the ipsilateral retina. The densest terminal field in the intergeniculate leaflet is from the contralateral retina, which completely overlaps the ipsilateral projection. Most nuclei of the pretectum receive innervation largely, but not solely, from the contralateral retina, although the olivary pretectal nucleus has very dense patches of innervation derived exclusively from one retina or the other. Retina-dependent variation in terminal field density within the three closely examined nuclei may indicate areas of specialized function not previously appreciated. This issue is discussed in the context of the melanopsin-containing retinal ganglion cell projections to several nuclei in the circadian visual system.

Histological evaluation of the lesion induced by inoculation of Leishmania mexicana in the cheek pouch of the hamster / Avaliação histológica da lesão induzida pela inoculação de Leishmania mexicana na bolsa jugal do hamster

We have studied the role of the immune response in the morphology of the leishmaniotic granuloma induced in the cheek pouch of hamsters, an immunologically privileged site, after inoculation of 3 x 105 Leishmania mexicana. Animals were histologically and immunologically evaluated until 120 days after inoculation. Independent of the time of sacrifice, the animals were always non-reactors to the footpad test (FPT). At histology, the introduction of L. mexicana in the cheek pouch leads to an abscess that evolves to a granulomatous reaction rich in amastigote forms, and later it leads to resolution, even in the absence of immune response detectable by FPT. Our results demonstrate that the development of immune response is not preponderant for the control of infection induced by L. mexicana inoculated subcutaneously in the cheek pouch of the hamster. It also suggests that the macrophages present in the leishmaniotic granuloma are capable of eliminating this parasite, even in the absence of immune response evaluated by FPT.

No presente estudo, investigamos o papel da resposta imune na morfologia do granuloma leishmaniótico induzido na bolsa jugal do hamster, um local imunologicamente privilegiado, após inoculação de 3x105 Leishmania mexicana. Os animais foram avaliados histológica e imunologicamente até os 120 dias da inoculação. Independente da época do sacrifício, os animais foram sempre não reatores ao teste do coxim plantar. Histologicamente, a inoculação de Leishmania mexicana na bolsa jugal resultou na formação de abcesso que evoluiu para reação granulomatosa rica em formas amastigotas e, posteriormente, para resolução. Esses resultados sugerem que o desenvolvimento da resposta imune não é preponderante no controle da infecção induzida pela Leishmania mexicana inoculada subcutaneamente na bolsa jugal do hamster. Sugerem ainda que os macrófagos que compõe os granulomas leishmanióticos são capazes de eliminar esse parasita, independente da presença de resposta imune avaliável pelo teste do coxim plantar.

Distribution of substance P and neurokinin-1 receptor immunoreactivity in the suprachiasmatic nuclei and intergeniculate leaflet of hamster, mouse, and rat.

The circadian pacemaker in the hypothalamic suprachiasmatic nuclei (SCN) receives photic information directly via the retinohypothalamic tract (RHT) and indirectly from retinally innervated cells in the thalamic intergeniculate leaflet (IGL) that project to the SCN. Using standard immunohistochemical methods, we examined the presence and distribution of substance P (SP) and the neurokinin-1 receptor (NK-1) in the SCN and IGL of rat and determined whether the patterns of immunostaining generalized to the SCN and IGL of Syrian hamster, Siberian hamster, and mouse. Terminals immunoreactive for SP were sparse within the SCN of Siberian and Syrian hamsters and mouse but were intense in the ventral, retinally innervated portion of the rat SCN. Immunostaining for the NK-1 receptor was mainly absent from the SCN of hamster and mouse. In contrast, a plexus of NK-1-ir cells and processes that was in close proximity to SP-ir terminals was found in the ventral SCN of the rat. Substance P-ir terminals were observed in the IGL of all four species, as were NK-1-ir cells and fibres. Double-labelled IGL sections of hamster or rat revealed SP-ir terminals in close apposition to NK-1-immunostained cells and/or fibres. These data indicate that SP could be a neurotransmitter of the RHT in rat, but not in hamster or in mouse, and they highlight potential species differences in the role of SP within the SCN circadian pacemaker. Such species differences do not appear to exist at the level of the IGL, where SP-ir and NK-1-ir were similar in all species studied.

Evidence of neuroanatomical connection between the superior cervical ganglion and hypoglossal nerve in the hamster as revealed by tract-tracing and degeneration methods.

Previous studies have shown the existence of a sympathetic component in some cranial nerves including the hypoglossal nerve. In this study, the horseradish peroxidase (HRP) tract-tracing retrograde technique and experimental degeneration method were used to elucidate the possible neuroanatomical relationship between the superior cervical ganglion (SCG) and the hypoglossal nerve of hamsters. About 10% of the SCG principal neurons were HRP positive following the tracer application to the trunk of hypoglossal nerve. Most of the HRP-labelled neurons were multipolar and were randomly distributed in the ganglion. When HRP was injected into the medial branch of the hypoglossal nerve, some of the SCG neurons were labelled, but they were not detected when HRP was injected into the lateral branch. The present findings suggest that postganglionic sympathetic fibres from the SCG may travel along the hypoglossal nerve trunk via its medial branch to terminate in visceral targets such as the intralingual glands. By electron microscopy, the HRP reaction product was localised in the neuronal somata and numerous unmyelinated fibres in the SCG. In addition, HRP-labelled axon profiles considered to be the collateral branches of the principal neurons contained numerous clear round and a few dense core vesicles. Besides the above, some HRP-labelled small myelinated fibres, considered to be visceral afferents, were also present. Results of experimental degeneration following the severance of the hypoglossal nerve showed the presence of degenerating neuronal elements both in the hypoglossal nucleus and the SCG. This confirms that the hypoglossal nerve contains sympathetic component from the SCG which may be involved in regulation of the autonomic function of the tongue.

Structural features of mossy cells in the hamster dentate gyrus, with special reference to somatic thorny excrescences.

We have recently revealed that large multipolar neurons, presumed mossy cells in the hamster dentate gyrus (DG), were calretinin (CR)-immunoreactive (IR) at the ventral level, although these neurons were CR-negative at the dorsal level. In the present study, we confirmed this identification with several methods and analyzed structural features of hamster mossy cells in detail. Golgi impregnationi and intracellular Lucifer yellow labeling studies revealed that mossy cells in the hamster dentate hilus had extraordinarily prominent thorny excrescences on their somata as well as on their proximal dendrites. Mossy cells exhibited dorsoventral differences in their structural features; proximal dendrites of single mossy cells were fewer, and thorny excrescences were larger and more complicated at the dorsal level than at the ventral level. Electron microscopic serial section three-dimensional reconstructions revealed that somatic thorny excrescences consisted of large and complicated spines, which received numerous asymmetrical synapses from mossy fiber terminals. In addition, our confocal laser scanning microscopic observations also revealed many glutamic acid decarboxylase-immunoreactive punctae abutting the mossy cell somata and dendrites. Our present and previous observations revealed the structural features of hamster mossy cells and their differences along the dorsoventral axis and further indicated that mossy cells were prominently different in their chemical and morphological features among species.

Age-related changes in the hamster epididymis.

Reproductive ability is decreased in aged animals and in men. Little is known about the changes taking place in the epididymis, and the possible influence on the loss of sperm quality. We studied the age-related alterations in the epididymis and in epididymal spermatozoa of hamsters. Adult (6-month-old), middle-aged (18-month-old), and aged (24-month-old) hamsters were used. Serum samples were obtained to determine testosterone levels. Testes and epididymides were removed and studied by light and electron microscopy. Epididymal sperm was also obtained and the motility, position of cytoplasmic droplet, and concentration were evaluated. Measurements of the height of the epithelium, length of stereocilia, external tubular diameter, and thickness of the muscular wall were performed. The proliferative activity was also studied. An ANOVA analysis was used to compare quantitative differences between epididymal zones and age groups. Aged hamsters presented involutive changes in the epididymis. A decrease in tubular diameter was found in cauda; principal cell ultrastructure showed changes including the appearance of damaged mitochondria, bundles of filaments, and the accumulation of lipofuscin. Some clear cells showed an unusual morphology by the presence of large electrondense vacuoles. A reduction in sperm quality was also observed, including a decrease in sperm motility and concentration, and alterations in the migration of sperm cytoplasmic droplet. Testosterone levels and cellular proliferative activity did not change. Aging causes a morphological alteration of hamster epididymis (mainly in the cauda), and a decrease in sperm quality.

Effect of intralesional treatment with lidocaine and glucantime in hamsters infected with leishmania (viannia) braziliensis

Se estudia comparativamente el efec por vía intralesional de la lidocaina y el glucantime sobre lesionesde hámsteres experimentalmente infectados con leishmania (viannia) braziliensis. Los resultados revelan que todos los fármacos ensayado reducen significativamente (p<0,001) los tamaños promedios de las lesiones de los animales experimentales en comparac

Stereological estimation of number and volume of pulmonary neuroepithelial bodies (NEBs) in neonatal hamster lungs.

The number and volume of pulmonary neuroepithelial bodies (NEBs) of 1- and 4-week-old hamsters were estimated using unbiased stereological principles and systematic sampling techniques. For comparative purposes, volume estimations were also made in the carotid body, the parathyroid gland, and the adrenal medulla. A significant decrease was found in the total number of NEBs, immunoreactive for CGRP, between 1 and 4 weeks. Individual as well as cumulative NEB volume also decreased significantly. The cumulative NEB volume in 1-week-old hamsters was in the same range as the volumes of the carotids and parathyroids in the same animals. The postnatal decrease of the NEB number suggests that the NEBs are of primary potential importance in the neonatal stage, when they may complement the chemoreceptor function of the carotid bodies, which are relatively inactive at birth. Since the cumulative NEB volume (at least at the age of 1 week) is equal to that of the carotid bodies and the parathyroids, their physiological function may be of similar importance.

Inoculaçao de Mycobacterium leprae na bolsa jugal do hamster / ?

A utilizaçao da bolsa jugal do hamster na hanseníase experimental, foi avaliada por meio da inoculaçao de 6,0x101 8 M. leprae/ml no seu tecido subepitelial em 60 animais, empregando como grupo de controle, 12 hamster inoculados no coxim plantar. Os animais foram sacrificados 20 e 48 horas e 7, 14, 21 e 28 dias p.i. A evoluçao da lesao de inoculaçao foi anlisada pelo exame histológico em cortes corados pela hematoxilinaeosina e Faraco-Fite. A avaliçao da viabilidade bacilar na bolsa jugal do hamster foi realizada 7, 14, 21 e 28 dias p.i. pelo teste de recuperaçao dos bacilos em camundongos. Os resultados nos permitiram concluir que: a) a resposta inflamatória inicial ao M. leprae na bolsa jugal foi exsutativa e inespecífica, com duraçao curta;

'Hamster-like' cycles in testicular size in the absence of gonadotrophin secretion in HPD rams exposed to long-term changes in photoperiod and treatment with melatonin.

Long term changes in the secretion of FSH, LH and testosterone, and the size of the testis were measured in groups of hypothalamo-pituitary disconnected Soay rams (HPD rams, n = 8) and control Soay rams (HPD-sham operated and unoperated, total n = 8) while exposed to an artificial lighting regimen of alternating 16-weekly periods of long days (16L: 8D) and short days (8L: 16D), and when treated with a constant-release implant of melatonin given under long days (total study: 136 weeks). Short term provocation tests using NMDA (glutamate receptor agonist), GnRH and LH were used to assess functionality of the hypothalamus, pituitary gland and testis, respectively. Control rams expressed normal photoperiod-induced cycles in the reproductive axis. Blood concentrations of FSH, LH and testosterone were significantly increased under short days, and decreased under long days with parallel changes in testicular diameter. Treatment with implants of melatonin under long days mimicked the effect of short days and induced rapid reactivation of the reproductive axis. In the HPD rams the blood concentrations of FSH, LH and testosterone declined immediately after the HPD surgery and values remained close to the lower limit of detection of the radioimmunoassays throughout the experiment. LH pulses were absent in the HPD rams and NMDA failed to induce LH secretion consistent with functional disconnection of the pituitary gland from the hypothalamus. The testes regressed to a significantly smaller size in the HPD rams compared with controls even at the nadir of the sexual cycle (testis diameter: 30.2 +/- 0.7 vs 41.3 +/- 0.8 mm, HPD vs control rams, respectively). A low amplitude cycle in testicular diameter (peak to nadir: 5.0 +/- 0.7 mm) persisted in the HPD rams with a temporal pattern opposite to the controls (growth under long days instead of short days; 'hamster like'). In the HPD rams, the treatment with melatonin blocked the long day-associated increase in testicular size, without effects on FSH, LH and testosterone secretion, pituitary responsiveness to GnRH (LH increment) or testicular responsiveness to LH (testosterone increment). This was in contrast to the cyclical changes in all parameters induced by melatonin in the control rams. At post-mortem, the reproductive tract in HPD rams was markedly regressed compared with the controls. The efficiency of spermatogenesis was reduced with few germ cells maturing beyond primary spermatocytes. Immunocytochemical staining, however, revealed the maintenance of androgen receptor expression in Sertoli cells, pertibular cells and Leydig cells, and steroid activity as measured by 17 alpha-hydroxylase expression in Leydig cells. Overall, the absence of photoperiod-induced changes in gonadotrophin secretion in the HPD rams illustrates the dependence on regulation by the hypothalamus, presumably through the secretion of GnRH. The residual cycle in the size of the testes in the HPD rams was closely correlated with the photoperiod-induced changes in prolactin secretion which persisted in these animals (summary of previous published data included). The combined results support the view that melatonin acts in the hypothalamus to mediate effects of photoperiod on gonadotrophin secretion and in the pituitary gland to mediate effects on prolactin secretion (dual site hypothesis), and that FSH, LH and prolactin act synergistically to regulate the long-term cycle in testicular activity in the ram.

Selective neurite outgrowth of cultured cortical neurons on specific regions of brain cryostat sections.

During development, axons of the mammalian cerebral cortex show a high degree of selectivity in their growth into specific regions of the central nervous system (CNS). A number of studies have shown that growing axons are guided by permissive or inhibitory membrane-bound molecules. Cryostat sections of the developing brain provide a useful assay to investigate possible membrane-bound guidance cues because such cues are retained in their normal in situ locations in specific regions of the CNS. Moreover, cryostat sections can also be subjected to various treatments that affect membrane-bound molecules. Therefore, to determine the ability of such cues to regulate the growth and guidance of cortical neurites into specific brain regions at different stages of development, we used an in vitro assay system in which explants from newborn hamster cortex were plated onto various regions of cryostat sections from developing and adult hamster brain. Neurite outgrowth from cortical explants onto the cryostat sections was visualized with a fluorescent vital dye. Results showed first that cortical neurites grew robustly on neonatal cryostat sections but only sparsely on sections from adult hamster. Second, cortical neurites grew preferentially on regions of the neonatal sections such as the cortex, basal ganglia, brainstem, thalamus, and colliculus, which are either pathways or targets for cortical axons in vivo. In contrast, cortical neurites avoided growing on the cerebellum and olfactory bulb, which are neither targets nor pathways for cortical neurites in vivo. Results also showed that cortical neurites extending onto cortical regions of neonatal sections preferred to grow along the radial axis of the cortex. Finally, heat treatment of the neonatal sections drastically reduced cortical neurite outgrowth. Taken together, these results suggest that the growth and guidance of cortical neurites is influenced by substrate-bound, developmentally regulated, heat-sensitive guidance cues preserved in the cryostat sections.